(1) Field of the Invention
This invention relates to a process for producing a polymeric-type film or coating in the surface of cellulosic fiber.
(2) Description of the Prior Art
The use of radiofrequency generated plasmas to alter properties of fabrics, yarns, and fibers is known in prior art. However, no mention of the formation of polymeric material in the fiber surface by use of radio-frequency generated ammonia plasma has been found.
Low-temperature, low pressure plasmas are especially suited for modification of natural polymers, Jung, H. Z., Ward, T. L., and Benerito, R. R., Effect of Cold Plasma on Water Absorption Cotton. Textile Res. J. 47, 217-222 (1977); Pavlath, A. E. and Slater, R. F., Low Temperature Plasma Chemistry I. Shrinkproofing of Wool, Appl. Polym. Symp. 18, 1317-1324 (1971); Riccobono, P. X., et al., Plasma Treatment of Textiles; A Novel Approach to the Environmental Problems of Desizing, Textile Chem. Color 5 (11), 239-248 (1973); Stone, R. B., Jr. and Barrett, J. R., Jr. U.S.D.A. Study Reveals Interesting Effects of Gas Plasma Radiations on Cotton Yarn, Textile Bull. 88, 65-68 (1962); Ward, T. L., Jung, H. Z., Hinojosa, O., and Benerito, R. R., Effect of RF Cold Plasmas on Polysaccharides, J. Surface Sci. 76, 257-273 (1978).
These "cold" plasmas are generated by gaseous electric discharge, provide a source of high-energy electrons without excessive heating, and are highly reactive chemically. Free electrons receive energy from the radiofrequency (rf) electric field and through collision with neutral gas molecules, generate new chemically-active species of atoms, ions, and free radicals. In contrast to thermally-induced reactions, where energy is usually equally distributed among all particles in the system, energy in plasma reactions is supplied principally to the free electrons. Electron temperatures may reach 10.sup.4 K, but surroundings remain near ambient. Since plasma particles penetrate only to about 100 mm, the technique can affect the surface of polymeric materials without altering their bulk properties.
In 1960 Goodman, J., Dielectric Coated Electrodes, U.S. Pat. No. 2,932,591 (April 1960); Goodman, J., The Formation of Thin Polymer Films in the Gas Discharge, J. Polym. Sci. 44, 551-552 (1960), deposited extremely uniform and pinhole-free polymer films on glass and other nonconducting substrates by polymerization of monomer vapor in a gaseous electric discharge. In 1962 Stone and Barrett, Stone, R. B., Jr., and Barrett, J. R., Jr., U.S.D.A. Study Reveals Interesting Effects of Gas Plasma Radiations on Cotton Yarn, Textile Bull. 88, 65-68 (1962), showed that glow-discharge treatment of cotton yarn increased its water absorbency and strength. More recently (1971) Coleman grafted acrylic acid to polymeric substrates, Coleman, J. H., Method of Grafting Ethylenically Unsaturated Monomer to a Polymeric Substrate, U.S. Pat. No. 3,600,122 August 1971), on which were created free-radical sites by moving the substrate through a spark discharge in a zone of initiator gas. Pavlath and Slater, Pavlath, A. E. and Slater, R. F., Low Temperature Plasma Chemistry I. Shrinkproofing of Wool, Appl. Polym. Symp. 18, 1317-1324 (1971), found that exposure of wool to low-temperature plasmas increased strength and abrasion resistance while reducing felting shrinkage. We have previously reported, Jung, H. Z., Ward, T. L., and Benerito, R. R., Effect of Cold Plasma on Water Absorption of Cotton. Textile Res. J. 47, 217-222 (1977); Ward, T. L., Jung, H. Z., Hinojosa, O., and Benerito, R. R., Characteristics and Use of R. F. Plasma-Activated Natural Polymers, Appl. Polym. Sci. 23, 1987-2003 (1979); Ward, T. L., Jung, H. Z., Hinojosa, O., and Benerito, R. R., Effect of RF Cold Plasmas on Polysaccharides, J. Surface Sci. 76, 257-273 (1978), studies of the effect of rf plasmas of argon, nitrogen or air on a group of polysaccharides that included cotton and purified cellulose.